The Armenian hamster has been employed in conventional cytological experiments to reveal induced reciprocal translocations in F1 offspring, as well as a new and unique class of latent mutations. Mutagenic studies with agents which induce non-lethal chromosome rearrangements may lead to methods for the precise cytogenetic evaluation of known and suspected mutagens. Latent mutations induced by ancestral exposure to known mutagenic agents is a new class of mutational events which, otherwise, remain undetected by assay systems usually employed for the evaluation of potential environmental mutagens. The possibility that some mutagens may also prove to be carcinogenic can be explored in the same mammalian system in parallel assays for evidence of carcinogenic activity in normal Armenian hamsters, and for carcinogenic potentiation in particular translocated heterozygotes. Approach: A series of candidate and known mutagens will be assayed for the induction of latent mutations, and for their activity in bringing latent mutations to completion as follows: Candidate mutagen: followed by urethan treatment; (known latent mutagen, such as EMS, serving as control; followed by urethan treatment), and Known Inducer of latent mutagen: followed by candidate mutagen to provide information with respect to activity of candidate mutagen as: (1) an inducer of latent mutations; and (2) as an activator of previously existing mutations. Cytologically normal F1 offspring from matings between fathers treated with potential mutagens and normal mothers will be mated to normal counterparts. The resulting F2 male population, following another cytological examination by means of unilateral orchidectomies, will then be treated with low energy yielding alkylating agents, such as urethan (100 mg/kg), and examined daily for at least two weeks to determine latent cytological anomalies and specificity of breakage sites, as described in the original experiments employing ethyl methanesulfonate and urethan (Lavappa and Yerganian, 1971).